Evolution of Rockfolk

Question

contrary to popular belief Rockfolk are not actually living rocks but rather a animal that coat themselves in rocks and stones. some basic characteristics of these Rockfolk include:

• have extremely sensitive skin, and are completely hairless
• are fairly slow, with short and stocky legs
• are bipedal
• have a average lifespan of 40 years
• coat themselves with rocks (either applying them with a naturally produced mucus, mud or wet clay)
• are 8 feet in height
• are herbivorous but also ingest pebbles to help with digestion (similar to some birds)
• have proportionally longer arms
• live in small, tightly knit tropes
• have rhino level vision, but have a decent sense of smell and elephant level hearing
• are quite bulky with gorilla level strength
• are smarter than a rhino

Given these characteristics, what species could they have evolved from, and what evolutionary pressures would lead to them?

Answer 1

Most of these are features of a lot of big animals so that's nice. This is far enough from any species I know of that you've got a lot of free-rain on what vertebrate to evolve from, just give it plenty of time. The fastest paths would probably be mammals and theropods (the group of dinosaurs that includes birds). I do have a couple of concerns:

1. Rocks on weak skin is a bad combo. Maybe strengthen then skin and make them use the rocks for camouflage (maybe they have bright mating displays to cover up) or UV protection (like hippos). Or only use clay-based mud.

2. The long arms/small legs/bipedal combo is weird and you'll need a good reason for it. Arms that are longer or stronger than legs are rare in the first place, the only examples I've got are bats, birds, and pteresaurs (because wings are difficult). Bipedal animals usually have big strong legs because the they need to support their body. And why would it not go back to being a quadruped if the arms are strong? So we need one of these features to be vestigial and another to be evolved from their current use. Bone sizes change easily so it wouldn't keep this trait long and we need to evolve long enough to fix #1. Okay, how about you evolve it from a bipedal species, but it tends to stay planted in one place so it evolved long, but relatively weak arms to reach dirt and food from its spot. The arms are too strange in size to walk on or support its body weight so when it does move it uses bipedalism still but those legs have shrunk from their previous size so that they're only good for finding a new perch.

Answer 2

It is not unheard of. Caddisfly larve, hermit crabs and some deepsea creatures decorate and protect themselves with debris. It is a little stretch, but it might be possible that a larger land creature starts adding it to his fur/slimy exterior as they don't need to grow the exterior themselves. They eventually lose the fur if any, relying only on the stones and debris. It does pose some problems for the skin health though, so a few extra biological things have to be overcome. Infections and such might be overcome by the stickly layer being anti bacterial.

Still, you need to have good options against overheating, alternative of breathing through skin, protection against chafing of the stones, less flexibility in most covered parts.